Question 1129107
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The two computers together do 1/20 of the job each minute; the slower computer does 1/45 of the job each minute.  So the fraction of the job done by the faster computer each minute is<br>
{{{1/20-1/45 = 9/180-4/180 = 5/180 = 1/36}}}<br>
So the time required for the faster computer to do the job alone is 36 minutes.